The present invention relates generally to apparatus for reading bar codes or similar codes and more specifically to techniques for distinguishing the code from other data or markings.
A bar code is a pattern of bars of various widths or heights used to encode information. Bar codes are familiar from supermarkets and other retail stores, where they are commonly placed on the packaging, containers, or sales tags for items being sold to encode the price and other information about the items. They are also used by the Postal Service, where they are applied to envelopes to encode the zip code. The bar codes assist greatly in the processing of these items because they can be quickly scanned and automatically decoded--in the above examples, for registering the price of the transaction or for routing the mail.
Known bar code readers require that the location of the bar code be determined prior to scanning. At an automated checkstand, for example, the location of the bar code is determined by the cashier, who then moves it past a fixed scanner or, alternatively, may pass a hand-held scanning wand directly over the bar code. In the post office, the bar code is placed on the envelopes in a predetermined location or field of limited extent, and the scanner is configured to extract only that location or field.
Besides automatic bar code detection, other approaches have also been developed to facilitate high volume and/or high speed processing of documents. One such approach is image processing, by which electronic images of entire documents are captured and stored in computer memory, and the desired information is extracted from the electronic images rather than from the paper documents themselves.
At present, automatic bar code detection and reading techniques cannot be readily combined with full-document image processing for automatically reading a bar code from a full-document image, unless the bar code is known in advance to lie within a predetermined field of limited extent and known position and orientation on the document. A typical image of an 81/2 by 11 inch document may contain about 500 Kbytes of pixel data, while the image of a bar code appearing on the document may require only about 2 Kbytes. Thus, the bar code image will be submerged in a sea of other pixel data.